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When do I execute a missed approach on a LOC approach when I can't identify the MAP?
According to AIM 5.4.21(b):

When an early missed approach is executed [...] fly the IAP as
  specified on the approach plate to the MAP at or above the MDA or DH
  before executing a turning maneuver.

Hence if a pilot decides on a missed approach, he needs to wait until over the MAP to execute any turns on that procedure. One can only assume that is meant to prevent a climbing turn into a nearby protected airspace.
The following scenario puzzles me.
A pilot executes a LOC approach with a missed approach consisting of "Climb to 1000' then left climbing turn to 5000' direct to..." Sometime after the FAF the cockpit timer breaks. The MAP can no longer be identified by time. The pilot immediately starts climbing to 1000'. But when to start the left climbing turn to 5000'?

The aircraft does not have other equipment that would positively identify the MAP, when is that pilot required to begin that turn?
What if the aircraft has a DME? Is the pilot allowed to identify the MAP by distance rather than by time?

Well, I’m not an FAA guy so I can’t find the relevant FAR quote, but going more general:
ICAO Doc 8161 Vol 1 - Aircraft Operations I-4-6-1
6.1.4 Note 2

In the case of a missed approach with a turn at an altitude/height, when an operational need exists, an additional protection is provided for the safeguarding of early turns. When it is not possible, a note is published on the profile view of the approach chart to specify that turns must not commence before the MAPt (or before an equivalent point in the case of a precision approach).

There is a nuance difference between AIM’s “you are not supposed to turn” and the ICAO’s  “if the turn area is not protected there must be a warning label”. The first is just procedural, the second ensures you will not hit a mountain.

If the missed approach only specifies ‘Climb 1000’ then climbing left turn to..’ then the airspace is protected even for early turns (between IAF and MAPt) and you can start turning as soon as reaching 1000’. It might get you in trouble with ATC (ie. they were not expecting you to do it), but it will not get you into a mountain side. If you can call ATC and explain that you are turning early because of a navigation/timing fault, you will be allright.
If there is also a ‘do not turn before [...]’ then you shouldn’t turn before, regardless if that fix is the MAPt or not. How to determine that fix or MAPt then becomes a navigation issue:can you use alternative methods? Gps? Dme? Vor radials? are you under radar contact? How about using the VSI climb rate to estimate 1 minute (climbing 700’ at 700 fpm). If neither, then you might be in an emergency situation.

Thanks. Ok if it makes my question easier to understand you could interepret the same question with an added missed approach plate instruction that "turns must not commence before the MAP". I'm pretty sure that instruction does not need to be explicitly on the approach plate. You are not supposed to turn until you are over the MAP, AIM 5.4.21 (b). You cannot start turning upon reaching 1000' if you haven't reached the MAP, that is incorrect.
Indeed it appears like my question yields => you are in an emergency situation. Several answers suggest so.

And just as a side-note, I'm putting this into a comment: I cannot find any equivalent in EASA regulations for this , which means at least in EASA airspace, you are not expected to continue to MAPt

On Question 2: If there is a functioning DME on the airplane, and there was a DME signal that could be used, that is, a DME at the localizer or a DME at a VOR that is aligned with the approach path, yes you could use that, but it almost certainly the approach itself would be a VOR/DME approach and you would be using DME as primary anyway, with timing as a backup if the DME craps out.
If LOC only, your next best option would be to use a crossing radial from a nearby VOR as your primary MAP indication, and if there is one available it's usually depicted on the plate (then there's GPS of course).
You should always have a backup source for the MAP, so if it was LOC only with no nearby VORs and no GPS, so that timing is the only option, I would be using two stopwatches, or a stopwatch and my own watch as a backup.
Which gets us to Question 1: I was (theoretically) foolishly relying on single source timing and that is now gone, with no other source.  Well, what else can you do but use common sense to do the best you can?  Start counting down verbally from the seconds remaining when the stopwatch failed, and may add a few seconds extra just for kicks.
If you are well above MDA, you have lots of obstacle clearance margin for the missed approach procedure so it's not such a big deal to overshoot the MAP a little bit before you start turning (you could be executing a missed while in the middle of a circling maneuver at MDA on the other side of the airport, so overshooting the MAP a littl bit on final before climbing, even at MDA, is really not a big deal from that standpoint), so I would err on the overshoot side when implementing my best guess countdown.  I'd be confident I wasn't going to run into anything.

Your comment about the missed during circling is not correct. The clearance slope for the circling missed starts at the MAP and assumes 200ft/nm climb, you need to circle back to the MAP or climb in a circle over the airport within the protected area to a suitable altitude before going missed. Generally about 500 feet above MDA for cat A or B at the far side of the circling area.(one mile runway+1.5mile protected area/ 32:1 climb slope)

I should add that I live in mountainous area and the missed obstacle clearance surface often determines the MDA or DA.

When there is a turn at the missed approach point, the protected area looks something like this (from the TERPS standards):

There are different diagrams for different situations, but except for missed approaches involving a 180 degree turn or close to it, they all have an unprotected area that you will cross if you turn too early. The diagram for a missed approach with a straight portion followed by a turn (below) is more complicated, but it still has the same feature that no obstacle clearance is guaranteed if you turn too early.

So you need to identify the MAP as best you can, and not turn until you are both past it and above 1000 feet. If you can't identify the MAP then this is an emergency situation, and you should use any and all measures at your disposal to identify it as best you can:

If you DME, VOR, RNAV, etc., and you can identify the fix that way, do so
If you are in radar contact with ATC, you can declare an emergency and ask them to identify the fix for you
If you know about how far you are from the fix, you can try your best to figure the time yourself. You can use the VSI and the altimeter for a fairly good estimate of the time elapsed. You'll need to convert the time you are away from the MAP for your new groundspeed if it changes significantly

Keep in mind that, since you started the climb early, you have a fairly large buffer to turn. If the MDA is 400 feet and it asks you to climb to 1000 feet, then the "Section 1" in the above diagram is about 3 nautical miles long. You can turn anywhere from 1 nautical mile before the MAP (more in some cases) to 3 nautical miles after the MAP and still have guaranteed obstacle clearance.

First, we know that the correct time to begin the turn in this case is when both conditions of having reached the MAP and climbed through 1000 have been met. We can climb as soon as we execute the missed. We can turn once we have climbed above the requisite altitude from the missed approach procedure and have laterally reached the MAP. We can reference Instrument Flying Handbook 10-21 under the section that explains how to fly a missed approach procedure, specifically as it relates to beginning the missed approach procedure and its requisite turns.
If the aircraft was equipped such that the timer was the only way to identify the MAP, look for available options outside your aircraft. If ATC has radar coverage, report the failure and ask for assistance identifying the MAP. If there is no radar coverage, notify ATC and do your best to estimate arrival at the MAP. When able, begin configuring the equipment you do have to follow the missed approach procedure which is left out of the hypothetical scenario. There is no official guidance on how to handle this exact equipment failure and situation. Much of it is subjective. The navigation that will be used in the missed would be helpful to the scenario, because as soon as you were able to navigate onto a radial, for example, you would no longer be in the dark about your position from the failed timer.
If the aircraft is equipped with DME, then the failure of the timer is only a loss of redundancy and you can still identify the MAP. DME is more accurate than timing the approach and should be the primary means of identifying the MAP if available.

Generally speaking the 1000feet would be the critical part and assumes no more than 200ft/nm climb unless a specific minimum climb grade is stated on the plate. If the following turn requires some obstacle avoidance they will give a heading to intercept a particular radial. Simply "direct to" implies that there is plenty of lateral clearance once above 1000ft(in this example).
If the approach VOR (or LOC) is on the airport, you can watch for station passage. If you know you are only 2 minutes into a 6 minute approach then count off 4 minutes while also climbing on course. Look at the MSA on the plate, once you get above that you can turn when you want. The approach plate will also give the controlling obstacle elevations.
Don't fly with a single cheap clock as your only source of distance navigation. The odds of this situation are extremely low even with a poor quality watch, but at some point the odds of a situation become so long that you can't justify another contingency plan.

No, you can go missed anytime you feel you cannot complete the approach you are currently flying successfully.  This includes anytime you are flying the final approach segment before reaching the VDP, if there is one, and all the way to the MAP at MDA.
If, at any time you can no longer identify where you are on an instrument approach because of an equipment malfunction, that’s an emergency situation.
I will also point out that the cockpit timer is not required equipment aboard an airplane for IFR operations. The only thing you’re required to have is a clock with a second hand in order to time the approach (§91.205 (d)(6)).
A failure of a required piece of equipment needed to fly the approach properly would be a mandatory reason to execute a missed approach immediately.  If you don’t know where you are, you are swimming in very dangerous waters and your first step is going to be getting away from the ground ASAP.  Now if stepdown fixes can be identified by multiple means, then there is some redundancy, unless a piece of equipment eg DME, etc is specifically listed on the plate as required for the approach.

AIM 5.4.21 specifically mentions the requirement not to fully execute a missed approach on a final approach segment until the MAP is reached. Climbs seem permitted, but turns are not.

It would depend on what cause the need initiate the missed approach.  In addition, unless comms are lost or some other reason, you usually will not fly the full missed approach procedure but will be handed over to approach controllers who will assign vectors.

Assuming you have radar service. That's probably worse than being fully dependent on the magenta line.

This doesn't answer the question.

Yes it does answer his question.


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How much clearance is provided when taking off over a 50 foot obstacle?
When performing a takeoff over a 50' obstacle, how much clearance is provided between the obstacle and the aircraft and where can that be found?

Which class of aircraft are you inquiring about? The answer may be different between airliners and sports aircraft.

Calculated figures for take-off distance required (TODR) are to only just clear a 50-foot obstacle at that distance (with gear down), and figures provided by aerodromes for take-off distance available (TODA) are the measured distance to the obstacle, with no extra clearance added.
If there's any uncertainty when they measure TODA, they'll give the most pessimistic value. The obstacle may be further away than the given TODA but no closer. Measuring distances is easy with modern equipment so it's likely to be an exact figure. However, it's rare for the first obstacle to be exactly 50 feet high. If the obstacle is (say) only 30 feet high, you get 20 feet of separation for free.
Be sure to apply the standard safety factor (e.g. 1.33) when comparing your calculated TODR with the published TODA, to ensure you get plenty of separation over the obstacle. As StephenS points out, if there are any significant obstacles in your take-off path, it's good practice to go for a best-angle climb until you overfly them.

Please don't confuse the purpose of TODA.  It is used for multi engine airplanes only that use unbalanced field lengths.  By definition it is not a value to the nearest obstacle.  See AIM 4-3-6.

The answer is provided in FAR Part 23.  There is no conservatism involved.  The distance provided is what the airplane can do.

§23.2115 Takeoff performance.
(b) For single engine airplanes and levels 1, 2, and 3 low-speed multiengine airplanes, takeoff performance includes the determination of ground roll and initial climb distance to 50 feet (15 meters) above the takeoff surface.

There is no specific clearance height since the takeoff distance, runway length, etc. will vary widely.  The point of calling out that scenario in training is to get pilots used to thinking about obstacles at all and, when obstacles do exist, make it a habit to climb out at best angle until clear of said obstacles (even though that may be just a few seconds if only 50ft) rather than automatically climbing at best rate as they're used to.

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What airfoil type is used on the B727-200F?
What airfoil type is used on the Boeing 727-200F? Is it a NACA profile or something else?

My favourite book for questions like this is Obert’s Aerodynamic Design of Transport Aircraft. It shows pressure distribution on the 727 wing and gives some AIAA papers as sources. If you track these down, that might reveal more. Unfortunately no airfoil reference is given; however it is very likely that the 727 uses a proprietary Boeing airfoil.
Posting as answer despite not really answering, as it is still more than a comment...

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In a Boeing 767, what percentage of the aluminum is in structural components?
For a Boeing 767 (model year 2000), does anyone know how much aluminum is in 'structural' components, as a percentage of the total amount? And specifically the wings?

I'm guessing that you're asking, "Out of all of the structural material in the aircraft, what percentage of it is aluminum?" Is that correct?

Total structure, at first sight 80%. (source)

For the structural wing box, upper plank, lower plank, front and rear spar webs, and ribs, it's going to be pretty much all aluminum except some of the fasteners (Hi Lite or Hi Shear steel pin rivets in some areas).  I would think over 90% aluminum alloy of some kind.

Welcome to aviation.SE! I edited your question to hopefully make it a little clearer. If I made a mistake, you can edit again yourself or roll back the change. If you're new to StackExchange, the [tour] may be helpful to see how the site works.


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How far could the Wright brother's catapult have thrown their unpowered plane?
I know that the Wright brothers started to use a catapult in September 1904 to help their Flyer II take off easily even when no headwind was available.
Assuming the propellers did not turn, or they were not even mounted on their shafts, how far away the catapult could have thrown Flyer II together with its engine and pilot? 1m, 5m, 10m, 25m, 100m or more? Even a rough evaluation, based for example on an experiment with a scale model, would be good for me.
(Note: I am not interested in a pure ballistic evaluation, considering the plane the equivalent of canon ball of mass, m, that is accelerated to the speed, v, and launched at an angle alpha.)

I'm not sure that this experiment has been done with a scale model, are you actually asking that somebody build an accurate scale model and attempt to replicate this for your answer? Otherwise a purely ballistic answer or mathematical one is all you can hope for...

The catapult used 1400lbs of weights falling from a 20-foot tower for propulsion. Maybe somebody can do the math and figure out how much energy that imparts vs the performance of the Flyer

It appears that a Flyer II, with the engine stopped and accelerated only by that falling weight, could not have flown at all because the energy communicated by the weight to the plane is about the same as that required by the 925 lbs Flyer II to reach the take off speed (30 mph). --- E_weight=(1400 pound) * (20 ft) * (9.81 (m / (s^2))) = 37 975.87 joules --- E_plane_take_off=(925 pound * ((30 mph)^2)) / 2 = 37 732.25 joules. The moment the take off speed is attained, the weight stops, the aerodynamic friction diminishes the speed and the plane remains below the required 30 mph flight speed.

"thrown" is not the right word - it merely pulled the plane down a track for a distance. If the plane didn't get enough airspeed from the pull and the headwind, it wouldn't take off when the elevator was manipulated.

The catapult cannot launch an unpowered Flyer II at all.
Robert's comment reaches the right conclusion using potential to kinetic energy, though his frictionless answer up to takeoff overestimates available energy and depends on aero drag not to take flight. The corrections are:

All the potential energy from the weight is not transferred to the flyer. The weight builds kinetic energy that is dissipated as it slams into the ground. Its velocity is one third that of the flyer.
Though the tower is 20ft tall, the weight only falls 16ft(5m). The rope and weight take up space.

Setting potential energy of the weight equal to kinetic energy of weight and plane:
$$ M_w\cdot H_w\cdot g=\frac{1}{2}M_f\cdot V_f^2+\frac{1}{2}M_w\cdot V_w^2$$
$$635kg\cdot 5m\cdot 9.8\frac{m}{s^2}=\frac{1}{2}\cdot 408kg\cdot V_f^2+\frac{1}{2}\cdot 635kg\left(\frac{V_f}{3}\right)^2$$
$$130\frac{m^2}{s^2}=V_f^2$$
$$V_f=11.4\frac{m}{s}=25mph$$
Since the Flyer II needed 28-30mph to become airborne, the catapult cannot launch the unpowered flyer by itself, even excluding friction and drag.

The fact that the Flyer required 28-30 mph to become airborne just means that it required this speed for the lift to balance its weight.  A Flyer traveling at 25 mph would still presumably have a substantial amount of lift (just less than its weight), and would fly further—perhaps much further—than a simple ballistic trajectory.

@MichaelSeifert, the rail was neither sloping up nor elevated, so the Flyer traveling at 25 mph was still on the ground (ok, maybe a foot above it as the rail has some thickness), so it couldn't fly anywhere without climbing, and it couldn't climb at that speed.

The Wright catapult was powered by a 635 kg weight, dropped 5 meters.
It's potential energy, before dropping, mgh = 635 kg × 9.8 m/s^2 × 5 meters = 31115 Joules.
The 408 kg Flyer II  was connected to the drop weight with a compound pulley that moved it 15 meters when the weight dropped 5 meters.
Dropping the weight converted potential energy to kinetic energy as follows:
mgh × 2 =  drop weight mass (v)^2 + launch mass (3v)^2
drop weight speed = v
launch speed = 3v
The minimum flying speed was around 30 mph or 14.2 m/s
The catapult was mathematically evaluated with various launch masses, without friction or drag factors, using no gearing and 3x gearing for comparison:
Although the 1:3 gearing was a significant improvement in the catapult design, the 408 kg Flyer II was too heavy to reach launch speed, with a theoretical 11.4 m/s.
The much improved Flyer III, coming in at a svelte 323 kg, would come closer at 12.6 m/s.
Still too slow, with obvious solutions utilizing increased drop height, more drop weight, and still lighter aircraft design, why would the the Wrights hold below launch speed?
The answer may be in the other aspect of their development, the internal combustion engine.  Holding catapult launch speed down may have given them a crucial abort option, with the plane dropping to the ground a few feet from the rails with little or no damage.
With a more reliable engine, a more powerful catapult may have been more desirable.
With sufficient runway length, it is not needed.

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How do I get an airworthiness certificate for a prototype aircraft?
If I were to build a plane of my own design as a prototype for possible sales, what steps would I need to take to get an airworthiness certificate from the FAA? If it's truly a certified aircraft and not a homebuilt?

You are asking what the entire process of certification is? First thing you do is make one that you can run through the certification program, you can't certify an aircraft without building one first, then you have to fly it. Certification is a long, very expensive process. Until you get certification, your aircraft will be experimental.

I edited your question to make it a little clearer, I hope! If I got it wrong, please edit again or be just roll back to the previous version.

Actually I have a design that I believe would be commercially feasible. I understand that I would need to be part 23 compliant I understand that once the design was accepted that I would need a min of 3 prototypes. 21 for ground testing, I to fly and 1 for destructive testing of the design limits. I am under the impression that getting it from paper design so to speak to full certification would be between 2 and 5 mil. Is that anywhere even near a correct number?

@JoeDively You haven't said how big the aircraft is or how complex. An eight year old swag for a part 23 aircraft is $$25m for design and test and another $25m for certification. This does not get you a production certificate. https://generalaviationnews.com/2012/09/09/the-cost-of-certification/

You can't legally fly any aircraft heavier than an ultralight unless it is certified. Your prototype will be certified as Experimental Category in one of these classes. The certification is awarded based on inspection during construction, on completion, and after a flight test period. The design is not subject to FAA approval.
If you want to manufacture aircraft for sale, you need approval of the design. This is called a Type Certificate. For smaller general aviation aircraft the appropriate regulation is Part 23 which states the requirements. There are also Advisory Circulars which provide clarification on approved means for satisfying the design requirements.
To avoid the expense of inspecting and flight testing every aircraft as is required for the experimental category, manufacturers instead obtain a production certificate. This reference is for larger part 21 aircraft. The production process is approved rather than inspecting each aircraft as it is produced. Each aircraft is still flight tested, but this may take an hour or less as compared to an Experimental flight test, which is 40 hours.
Reading these four references will give you some limited understanding of what you are asking. Here is an 2012 swag at certification costs. Part 23 was estimated at $$25m for design and testing, then another $25m for certification. This does not get you a production certificate.

"You can't legally fly any aircraft unless it is certified." I'll point out that ultralights don't need airworthiness certifications.

@nick012000 You are correct.

Thanks Pilothead  Those articles and others related to the topic were very helpful. I guess me next step is to have a talk with the FAA about what I want to accomplish and see what they have to say.


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How did Airbus fit 6,340 gallons more fuel into the A359?
Bloomberg posted an article that says, among other things, the A350 ULR variant increases range by utilizing "additional space already available in the existing tanks to carry an extra 6,340 gallons of fuel."
What is the deeper technical explanation, or why not use this space in the regular A359 variant?

Bloomberg says minor changes to "piping and venting" made the capacity available. It came from previously unused space in the center fuel tank.

The a359 center tank filling point is not at the highest point in the tank, so it needs a vent in order to use that space. Without the vent, the tank airlocks and no more fuel will flow in.
Piping refers to changes to that tank's inerting system, designed to prevent explosion of fuel vapor in the tank. Inerting has been required for wingbox center tanks ever since TWA800. See Leeham for more detail, search the page for Update2.

As to why this is not part of every a359, it is operating cost. The regional variant has a 260t MTOW and therefore lower landing and navigation fees. The 280t MTOW needed for the ULR will be available from 2020 on the standard model, so there is very little difference otherwise. If you order the ULR you can paper change it to a regional, though I don't know anyone who would.
Leeham also has an interesting article on how seating (passenger weight) has to be limited to get maximum range from the ULR.

All fuel increases eat into payload. plane designs have a "useful load" and that useful load is divided between fuel load and payload. I don't know of any commercial planes that can get both full tanks(and full range) and their maxium rated payload at the same time. Also I would guess that maximum landing weight did not change with that increase from 260t to 280t mtow.


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Why aren't takeoff flaps used all the way up to cruise altitude?
In general aviation aircraft such as Diamond star DA-40, flaps to take-off are used until 500ft AGL and speed before retracting flaps is Vy (best ROC speed)-67kts and after retracting flaps is 80kts.
Why can't we use take-off flaps until cruise altitude such as 6000ft MSL and maintain 67kts and climb sooner?

This is a good question. I find the current answers not completely compelling, since they don't address whether it's generally better to climb as quickly as possible or to pick up airspeed and climb more slowly but with better ground and air speed. Constant factors, such as engine cooling prop pitch, and transient factors, such as winds aloft, enter into play.

Who says you can't?  You can climb all the way to cruise at Vx if you really want to...  ;)

The image below from  this answer shows characteristics of airfoils with flaps.
As you rightfully concluded, lift ($C_{L_{max}}$) goes up with the deployment of flaps, but the drag also goes up and even quicker than the lift. Increasing lift is good, but if it comes at the cost of more drag, it will require more thrust (therefore fuel) to maintain this higher lift.
Thus, the value we should maximize is the ratio of lift and drag. The ratio of the two $\frac{L}{D}_{@C_{L_{max}}}$ is also shown below, and it shows that the basic airfoil performs better than those with flaps.

+1 for mentioning L/D. Lift remains roughly constant (at constant weight), but if L/D is lower with flaps, the same amount of lift comes with more drag.

This is pretty much all there is to it. Flaps are simply a way to get initial height quickly, but sacrifising fuel doing so. Without flaps you would eventually get to your destination quicker and with less fuel, but you would take a risk taking off, and while we're at it, landing too.

@Jpe61 your comment is partially incorrect. The DA40 climbs faster with flaps down, so it is in fact more efficient if we are only concerning fuel burned vs. altitude. See https://aviation.stackexchange.com/a/89213/20394 for the numbers from the DA40's POH.

Oh,  I stand corrected in that sense. However, it climbs faster, but does it advance as fast as in clean config? Which configuration would produce a sort of an inverted brachistocrone?

@Jpe61 That's a great question! A real-world answer is really hard and can probably only be found through dynamic programming. If we assume a constant wind field as we climb, then we might be able to find a closed-form synthesis. If we assume a calm day, then an evaluation could be done by looking at the glide ratio: in one minute the flapped DA40 travels 912' less but climbs 110' more. The glide ratio is around 10:1, so that means it could glide 1100' extra. I take this to mean that in energy terms, it is marginally more efficient to climb at the slower air speed in still air.

This is a good question, and I don't feel the other answers get at the essential part which is:
Is it optimal to climb with the flaps deployed?
As with any optimal question, the answer relies on what it is we wish to optimize. It's worth examining two goal states:

To climb to altitude as quickly and efficiently as possible. For instance:

the winds aloft are so good that the pilot wants to minimize the time spent down low
the pilot would like altitude for aerobatics
the pilot would like to do high altitude testing

To go from point A to point B while employing best safety practices all while reasonably minimizing time and/or fuel costs.

Why use the flaps in the first place?
In general, getting off the ground and clearing any obstacles while remaining close to the airport is generally considered best practice, even if it means burning a little more gas. Depending on a number of design choices, the climb angle with flaps can be much improved, which means that obstacle clearance is better and in the event of a takeoff emergency the plane has a lot more runway in front of it, or it's not so far from the airport.
The advantages of taking off with flaps down:

Wheels leave the ground at a lower airspeed, eliminating rolling resistance. (It's surprising how much drag comes from those tires, esp. in grass and soft fields.)
Climb angle is better

From the DA40 manual, pgs. 5-14 and 5-16, STP climb rate with flaps is 9.7deg (1160fpm @ 67kts) and without is 7.8deg (1050fpm @ 76kts).

Climb rate might be better

So what are the disadvantages?
Increased drag at higher airspeeds
As @ROIMaison shows in this answer, for a Clark Y airfoil the L/D ratio with flaps deployed isn't even remotely close to the normal airfoil. At higher airspeeds this loss of efficiency is acutely felt.
Of course, the DA40 has a much more advanced airfoil and so the spread might be much closer together. Diamond's airfoils come from gliders, and gliders use flaps in low-speed flight in order to turn more quickly. As you might imagine, gliders are optimized for efficiency, so it's fair to reason that the flapped L/D ratio for DA40's airfoil is potentially much better than the venerable Clark Y's.
In case the link between drag and climb rate is not immediately obvious, the more drag there is the less surplus energy is available to increase the plane's potential energy, i.e. to climb.
Engine cooling
The engine cowling is designed to provide appropriate cooling at relatively high airspeeds. There's a certain thermal inertia which protects the engine for a minute or so, but after that temperatures start reaching critical points. It's important to nose over and pick up airspeed in order to improve cooling.
Propeller inefficiency at slower speeds[*]
For a fixed-pitch cruise prop, efficiency suffers quite significantly at lower airspeeds. Speeding up will gain some extra propeller and engine performance.
[*] Note that this doesn't apply to constant-speed props.
Conclusion
With the above in mind, we can see that the best practices of getting up off the ground quickly, with plenty of runway to spare, and with enhanced obstacle clearance is a Good Thing (TM). These goals are largely met by 500', so this is an opportunity to reevaluate our optimal process. Do we still want to climb, or do we want to go somewhere as well?
Unfortunately, I don't have any basic sense of whether it's generally optimal to continue to climb with the flaps deployed. It might even depend on the particular plane model whether absolute climb rate is better with flaps up or down. If the climb rate is worse with the flaps down, then the answer is clearly to get them up as soon as practical.
Supposing climb rate is better with flaps deployed, the situation doesn't really become clear. If the winds aloft are favorable, then getting to altitude quickly is valuable. But more valuable than proper engine cooling? Hmmm...

You say "advantages of taking off with flaps down: [...] Climb angle is better". Is that something special for the DA40? For example, in a B737 the exact opposite is the case and you actually want lower flaps when obstacle clearance is limiting.

@Bianfable in the video at 3m02s I see the image you're referring to. The short answer is I really don't know. The T/O flaps for the DA40 are 20 degrees, which is somewhat close to the 737's 25 degrees. But IIRC, turbines are very ineffective at slow speeds, so it's also possible the 737 looses a ton of efficiency if it flies slowly. Check out https://aviation.stackexchange.com/questions/49946/how-and-why-does-engine-thrust-change-with-airspeed to see why a turbojet could wind up lifting earlier but losing climb angle.

Thanks for including the numbers from the manual. It could be that the opposite is only true for jets. OTOH, the 737 limitations are based on the OEI (one engine inoperative) climb performance, where the relevant numbers here are for normal climb with both engines.

Because it would not be efficient. Flaps increase drag (and lift), so you would burn more fuel climbing to cruise altitude with flaps extended compared to if if you retract them.

This is incorrect in the case of the DA40 (and any other plane where the climb rate is higher with flaps deployed). At full throttle, its climb rate is higher with flaps in T/O position, so it will use take less time and less fuel to get to the target altitude. See https://aviation.stackexchange.com/a/89213/20394 for the performance numbers from the DA40's POH.

Regardless of the data in the manual, you'd have to redefine the word 'flap' to get a better climb rate with flaps down. Flaps will increase camber, means worse L/D, means more drag, means less excess thrust, means less climb rate. That's physics. The rest is conjecture. If they don't do that they are not Flaps

Most people fly in order to get somewhere, so cruise climb is used as it covers more ground while getting to altitude.
Here is the DA40 airspeed table that would have been nice to include in your question. Depending on weight, cruise climb speed is 6-9kt higher than takeoff climb speed. If your objective was just to gain altitude, as for local observation, you could use takeoff flaps if you wanted. In some aircraft you have to keep an eye on engine temps if you fly slowly at high power.

A better illustration is in transport aircraft where the speed difference is much higher. Here is the BaE146 takeoff sequence. There are speed limitations for deployed flaps, so retraction is structurally required as speed increases. Staying under a 135kt limit for takeoff wastes a lot of time when 220kt cruise climb is available and 250kt is the target.

Worth pointing out that for some aircraft, apparently not the DA-40, full or near-full flaps aren't optimal even for max ft/min rate-of-climb.  As others have mentioned, the DA-40 has flaps with good aerodynamics so the L/D ratio stays somewhat efficient, but on other aircraft the L/D ratio can be much worse with flaps out.

Flaps give you more lift, but also more drag. The drag means that your horizontal speed is lower.
The usual phases of flight where low speed is an advantage are:

When taking off from a runway. You don't want to run out of runway and you want to end wheel drag as soon as possible.

When trying to clear obstacles. You want as much time to gain altitude before you get to them.

When at low altitudes. You don't want to get too far away from the airport when your gliding range is low.

When near landing. You need to drop altitude but also keep your speed down.

When landing. You want to get as slow as possible before you touch the ground.

Flaps make the lift/drag trade-off worse for you. That's only sensible when the drag is a good thing or the extra lift is absolutely necessary.
Once the drag becomes a loss rather than a benefit and you have enough lift without flaps, the logic of flaps stops applying. You want the most efficient wing configuration with as little drag as possible for the lift generated. That's the configuration your wing was built for.

Flaps provides extra lift at lower airspeeds but for the cost of huge drag.
At some point the drag stops the plane acceleration and it cannot climb any faster.
Note that the airlines want as fast transport from Gate A(XYZ) to Gate B(HKL). Airports want as short runways as possible. Government wants as small noise-loaded areas as possible.
Short runway limits the take-off/landing speeds significantly so the wing setup must provide lift at low airspeeds even at the cost of drag.
The government demands as fast climbing as possible and from some altitudes the noise is spread so wide the ultimate climb rate is not mandatory and airlines are free to optimize for the most crucial parameter - cost.
Here the drag is the adversary so flaps are retracted. Plane can fly faster for smaller thrust needed and the thrust reserves can be used for nose-up climb as well.


text:
Why are the aircraft in this image parked this way?
Why are these parked asymmetrically? And how can a plane owner get to their plane if it's on the farthest end?
Image Source: Wikimedia Commons

I'm assuming someone cut out a load of plane models and spent an hour or two putting them onto a wee little runway model trying to work out how to fit them all on.

None of the answers seems to address the fact that they are parked asymmetrically because there are many different types and sizes of aircraft. If you're parking all the same kind of pane they fit better in a symmetrical pattern like this

@TomMcW Almost everything, including airplanes, fits better and probably symmetrically if given both enough planning and a handy order of arrival. It looks like they started at the right corner and did their best every time a plane arrived.

there's also photoshop.

given that at least some of the aircraft seem to have their registrations and other identifying features stripped, it could also be the parking of a junk yard/scrapper.

I just want to know the story on that black airplane.  I am curious.

@Jammin4CO not sure it's exactly the same livery, but there's a fair few private jets painted mostly black to look cool https://flyblack.com/

@llama Looks cool, but I'll bet it costs more to keep it air-conditioned in the tropics.  Just like cars or building roofs, you want light colors in hot climates (to reflect more light and thus heat), and dark colors in cold climates (to absorb light and heat).  Is it possible this particular plane came from somewhere much colder?

@expeditedescent This image predates the pandemic.

@Jammin4CO The original was photoshopped out and the purveyor of this image forgot to put a different one in?

They are not parked. The area is tilted and they all slid to the end.

@Jammin4CO It looks like one of the shadows lost its plane!

@fraxinus Citation needed. If you take mixed nuts in a jar and shake them, they won't end up in an ordered pattern.

This is what happens when there are more planes to park than can fit on the apron. They are parked asymmetrically to fit as many aircraft as possible into the smallest area.
The Parking
Airports have various procedures for parking depending on how long the aircraft are expected to be on the ground and the overall anticipated demand for parking space. At peak times of the year you have to book a parking spot at your destination. And as @Digital Dracula said, sometimes you have to go to another airport to park when there is not enough space left.
The Departure
In situations like this you can't just jump in your plane and fly away. It involves working with the airport to move your plane out of the jigsaw. This can take a few hours when the airport is very full, and is done very carefully by all involved.
They shuffle each aircraft out of the way sometimes moving the aircraft multiple time to replace the hole that yours has just made. The airports plan these movements ahead and place the planes in the expected departure order to minimize moves.

Extended parking need seems common in winter, and a recurring theme for papers: 2018, 2019, 2020. However planes are shown parked on the West apron (airport diagram), while the OP picture is for the main apron. Both may be used though.

If your photo had only one aircraft pinned behind or between two others, there would be another possibility: it's a repair shop, and the owner of the pinned aircraft hasn't paid their bill.
I've known repair shops which, in order to prevent sketchy or troublesome clients from simply taking their repaired airplane and flying away, trap it behind other aircraft (or in one case between two large trucks parked inches from the nose and tail!).
Certainly this is not the case in your specific image, but sometimes the answer to "how can an owner get to their plane if it's on the far end" is "they can't, on purpose".

This provides additional information but does not answer the specific question that was asked.  I will delete this answer if the community feels it best.

Please let the up/downvoters decide and do not delete this one. It does provide a different aspect to the question.

@SteveV. Thank you for bringing this answer. May you please provide an image here in comment how does repaired aircrafts are parked.

They did this to deal with an overflow of traffic at Anguilla (Clayton J. Lloyd ) International Airport during the 2013 holiday season.
It is very fortunate that you properly cited your image.  This makes it so that there is no need for speculation here.  When you follow the citation train it brings you back to https://www.airliners.net/photo/Gulfstream-Aerospace-G-IV/2393432/L
The photo's caption reads:

The ramp at St.Maarten gets very full around New Year, making it necessary for many business jets to fly over to Anguilla to re-park.

and if you follow the comments, an anonymous user who seems to be an authority on what happened here states:

The aircraft are parked according to departures after a while. At night when the aerodrome is closed, crews reposition aircraft and place them in order of departures. A tug is at the ready during operations and shifts them accordingly. They do it each year. Anguilla now has some additional parking, so I doubt it will look like this December 2014

So, in this exact case, they parked them asymmetrically because they can fit more planes in the space this way, but they did it in an "orderly" fashion such that they are organized left to right by departure time.

See also the interview from the head of the team which takes care of this business and repositions the aircraft in order of departure.

Sound like a fun situation if the tug has a technical failure ...

Anguilla airport!  It was my home base for awhile.


text:
What is this scoop found on the core of a PW1127G engine near the CC/turbine section?
The view is back to front, the scoop is at 10 o'clock on engine 1. What would be it's function? I need supportive literature as well if possible.

That scoop allows air to go through the Engine Air/Oil Exchanger which cools the engine oil with fan bypass air.
Engine oil that is cooled by the air/oil heat exchanger decreases the quantity of heat that must be moved from the oil to the fuel in the fuel/oil heat exchanger.


text:
What is the difference between "Bay" and "Stand"?
When should we use the word Stand and when Bay for ATC taxi clearance?

Do you have any example where you heard such word (I never heard "bay" neither read it in a transcript, but I'm not an aviation professional)?

The correct terminology for a place where aircraft park is stand or aircraft stand, where bay or parking bay is colloquial.
The official definition from the ICAO ANNEX 14/I Aerodromes is:

Aircraft stand. A designated area on an apron intended to be used for parking an aircraft.

This can be either a stand at a gate or a remote parking stand.
The correct use of the word bay is for a holding bay as defined in ICAO ANNEX 14/I Aerodromes as:

Holding bay. A defined area where aircraft can be held, or bypassed, to facilitate efficient surface movement of aircraft.

So you use the term stand for an area where aircraft park (i.e. shut down engines, load/unload cargo, (dis-)embark passengers, etc.) and you use the term bay for an area where an aircraft temporarily holds (typically with engines running).

There are some sources using the term bay for parking, but I would consider all of them more informal than the official ICAO definitions:

The ENAV (company providing air traffic control services in Italy) writes (emphasis mine):

[...] which guides it right up to the parking bay.

on the English version of their website, but this could also be a wrong translation from the Italian original.
The Thales Group (French aerospace company) writes (emphasis mine):

Tower ensures smooth and seamless aircraft control between TMA boundary and the parking bay.

which again might be result of incorrect terminology used by the translator.
This article by Qantas suggests that the term is actually used by Australian ATCs (emphasis mine):

PILOT: “Qantas 635...we will arrive on blocks at 1500. Have 2 UMs, 2 WCHRs, 1 will need assistance to a taxi. Request a parking bay please.”
MOCO: “Copy that Qantas 635. 2 UMs, 2 WCHRs. You are for parking bay 26...2...6. See you on the ground Qantas MEL.

The CAAS (Civil Aviation Authority of Singapore) is also using the term (emphasis mine):

the aircraft was also assigned the shortest possible route from the runway to the parking bay to minimise fuel consumption.

Related:

What is the difference between a Stand and Gate in Airports? How do they differ ?
What are the correct names of the parking spaces for turn-around?


text:
How to calculate the moment/torque at the center axis of a blade?
How do I calculate the moment/torque at the center axis (same plane with lift and drag force) of a blade with NACA airfoil standard when it is placed inside a wind tunnel or exposed to airflow?


text:
What are the bars protruding from this C-130?
This C-130 was photographed on approach to Ellington Field (EFD), Texas.

What are the protruding, truss-supported bars aft of and below the wing?

There's an airshow coming up in ~3 weeks at EFD, so it may have something to do with that, especially considering the fancy underwing paint job.

One word: chemtrails. Sometimes extra chemicals need to be spread, so they hook up the sprayer.

You must live really close to me.  I saw that guy doing patterns Sunday afternoon

I am fortunate to live in the neighborhood just SE of EFD, so we get the free airshow all the time.

@Tristan it's flying again today.

Saw it flying patterns again on Sunday 12/1.  Dude was LOW over my house

It is a civilian owned C-130 Hercules used for aerial spraying operations. It is owned by the International Air Response company based out of Mesa, AZ.

The aircraft is equipped with a RIDSS spray system for use in things like oil spill response (for spraying dispersants). You can read more about the system here.

Thanks! One of the pictures at the 2nd link clearly shows the spray-bar. https://internationalairresponse.com/wp-content/uploads/2015/09/d2.png


text:
Why does Pakistan continue to use F-16s?
Why does Pakistan continue to use F-16s even though they have their own JF-17s?
What features do Pakistani F-16s have which their JF-17s don't?

Because they're really expensive machines that still run well and are still highly capable?

The airframe of JF-17 is a lot less advanced than F-16(A), even though the electronics are a lot more contemporary.

Payload and Empty weight:
JF-17 has an empty weight of 14520lb while F-16A is 15600lb. However the maximum takeoff weight are 27999lb and 37500lb respectively. This means the mission consumables (fuel + armament) of JF-17 is only 60% of F-16A(13479lb vs 21900lb).
Powerplant
JF-17 is powered by RD-33/93 engine with thrust of 18285lb while F-16 is 27000lb. Again JF-17's thrust is only 2/3 of F16.
Fly-by-wire
To reduce cost JF-17 is only equipped with digital fly-by-wire (FBW) system in the pitch axis but F-16 has FBW on all three. This, together higher thrust, makes F-16 are more agile fighter.

JF-17 by design is a lighter and cheaper fighter than F-16, so it inherently has a relatively smaller range and payload capacity, which is unfortunately worsened by its excessive structural weight. Had PAF not maintained a number of heavier and more capable fighters, these short comings of JF-17 could be exploited to catastrophic levels by their potential enemies equipped with much more capable heavyweight SU-30s.
Apparently F-16s in PAF are showing their age and PAF has been seeking for replacements for a while, e.g. Chengdu J-10/FC-20 and Shenyang J-31/FC-31. However (IMO) due to PAF's tight budget neither are making any meaningful progress as of right now and the combo of JF-17 and F-16 seems sufficiently effective for the current status of geopolitics.


text:
What implications does automobile electrification have for the supply and cost of Avgas?
The electrification of automobiles has been picking up pace recently, with various countries and manufacturers setting targets for an electric- or electric/hybrid- only future.
If these plans come to fruition and are widely adopted, the demand for gasoline, and therefore its supply, would decrease considerably. While avgas is something of a specialty product, I would guess that it shares the bulk of its components, and their manufacture, with automobile gasoline.
Have there been any studies of the consequences of this change on the inflation-adjusted cost and its supply of avgas (though I imagine it will be available at some price), and also on motor gas for those aircraft that can use it?

While I think this is an interesting question, it's probably worth noting that especially personal transport by car is not the only place where motor vehicle-quality gasoline is used. Sure, it's a major part of the market, but not the only one. Also, it seems likely to me that both pure gasoline or diesel, as well as hybrid gasoline/electric, cars will be a part of the market (but perhaps a much smaller part of the new from the factory cars market than today) for a significant time to come.

There is also a push to move GA aircraft to Diesel (or Jet-A) which isn't going anywhere (not for a long time at least). If that happens, avgas will become rarer and older aircraft may become even more expensive to fly.

Crude oil contains a bunch of fractions, and the refinery has no choice which fractions they get.  They can't transmute the "good for gasoline" fractions into the "good for diesel" fractions, so if they are trying to make diesel they'll get a whole lot of gasoline as a waste product. Their only other choice would be to "burn it off" (in boilers to make process steam)... but the government doesn't like burning stuff needlessly... so the gov't will force them to produce gasoline for your Red Barchetta.

@Harper Firstly, note that the electrification of road transport is likely to diminish the demand for diesel as well, and also that a lot of gasoline is created by cracking: the ratio of refinery products today is far removed from what is in the crude. Nevertheless, you may have a point that gasoline becomes, once again, a side-product with more supply than demand, depending on what other uses there are for light fractions.

I have not seen any studies on this, nor would I expect to as Avgas is such a niche product and the price of it is not heavily dependent on the price of the underlying fuel itself. If you look at this answer the reason avgas is so expensive is that it has special requirements for making it, storing and transporting it and so little is produced that there's no economy of scale.
In any case your question is based on the premise that gasoline production is going to decrease. Even with the rise of electric cars most oil companies aren't forecasting a drop in gasoline demand until the 2030s, maybe even the 2040s as the increase in demand for new cars will oustrip the number of electic cars for some time. As a decline in consumption does not guarantee a price rise, any forecasts of this kind would be premature, and not likely to be reliable.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Why don't all commercial aircraft transmit GPS data in real time?
It seems strange that trucks and taxis can be set up to transmit GPS data in real time but aircraft cannot.  Wouldn't this be a useful function and feasible to implement?

Isn't this pretty much what ADS-B is?

Wouldn't it be easier to just have an iridium satellite phone on each airplane that could fire up a distress call in case of an emergency? I'm am not an aviation expert, but that seems like a easy solution.

This is obviously related to the recent downing of MH370. The limitation with something that will transmit data in real time is that it won't work if the antennae are destroyed. Most of the time it will work fine, but the times when you need it are the times it would be at most risk from destruction.

@Marcello Some aircraft do have satellite phones. However, the last thing a pilot is going to do in an emergency is fiddle with a bulky inconvenient phone.

@James some military aircraft did (and may still continue to) feature ejectable FDRs, e.g. the Tornado.

@james - how do you disconnect all the wiring taking power and data to the black box when you eject it? You can either have very flimsy connectors which might be broken in the very event you are trying to record. Or you could have explosive blades to sever all the cables - but this might not be a major contribution to safety

Just to be clear, its the Mode S transponder that transmits position from the aircraft. the SSR is on the receiving end.

@NobodySpecial - well, there are reliable, robust quick-release connectors available to replace the ubiquitous mil-circulars, (that we all hate anyway).

Most commercial aircraft transmit their GPS-based position twice per second. This is part of their Automatic Dependent Surveillance – Broadcast (ADS–B) broadcasts. The problem with providing world-wide receiver coverage for this system is that the frequency it uses only travels line via line of sight, so it won't travel past the horizon.
Providing coverage over large bodies of water would require a network of buoys, which would be quite expensive.
Another possibility is to put ADS-B receivers on satellites. This concept has been developed by (Aireon) on the Iridium Next satellite constellation. The system (66 satellites + 9 spares) became operational in 2019 and provides global coverage.

For one example of how ADS-B is being used, check out this FAA video -- they've made this work in the Gulf of Mexico because there are oil rigs to host receivers. Making it work over large bodies of water (like the oceans) is obviously more difficult as DeltaLima mentioned.

I don't think that the first sentence is really accurate.  There are a lot of commercial aircraft that don't have ADS-B....  The FAA isn't even requiring it on aircraft until 2020, and there are lots of areas where there is no ADS-B coverage.

@Lnafziger the first sentence is accurate, most (>50%) commercial aircraft have ADS-B (at least in my part of the world). It might not have been certified to the latest standards, but they transmit position.

@DeltaLima Maybe "in your part of the world", but that is only a portion of the commercial aircraft.  Also, if it is close to 50%, then "more than/around half" would be more accurate even if "most" is technically correct. :-)

@Lnafziger It was about 85% of Mode S transponder equipped flights 5 years ago, I don't have the recent number available, but it is certainly higher now.

@DeltaLima Fair enough, I was only responding to your comment which said ">50%".  :-)  There are still a lot (I would venture a guess to say most) non ADS-B aircraft here in the US though....  I think that this is a good answer, but would just like clarification on that statement since it is broad and seems off to me.

So according to FlightRadar24, 60% of passenger aircraft are equipped with ADS-B (70% in Europe and 30% in the US).  I'm not sure that I would call those "official" numbers but I think that it gives us a good idea.  (And we are both right, lol.)

@DeltaLima A slight addition: ADS-B has already been used aboard satellites, the European Space Agency's PROBA-V carries a receiver and has been very successful in using it.

Håkan Lans invented STDMA in the late 80's (patented STDMA '96) with a solution much smarter than the two you gave. Sometimes the industry and lobbyists really show their power. There is an ICAO standard for it (VDL Mode 4), but ADS-B is still the current standard. Similar story goes for ILS.

@sp1 True. PROBA-V was/is a technology demonstrator for ADS-B in space. The Aireon system is aiming to provide operational usable data.

@user VDLm4 is one of the three link technologies used for ADS-B, the others are 1090ES (wordwide standard) 978UAT (USA below 18000ft). Whilst the STDMA technology is far more advanced than the others (especially 1090ES), there are many reasons why it did not become the defacto standard. Lobbying had its role there, but there were a number of technical problems and legal concerns about the patent. The fact that new radio's had to be installed on aircraft didn't help either. At it's peak I think there were about 25 aircraft equipped with VDLm4 in Sweden.

May be worth updating with the fact that Aireon is now live

@J.Hougaard Thank you for the suggestion, I've updated the post. I am assuming you are a Danish ATCO,do you know if NAVAIR is already using Aireon data operationally?

@DeltaLima Not used in Denmark, no. But I imagine the main points of interest will be Greenland and possibly the Faroe Islands, where little or no radar coverage exists

@J.Hougaard It makes sense over there. Although there is already an ADS-B corridor over Greenland using terrestrial receivers, it has partial coverage. I was also thinking about the N sector over the North Sea for covering helicopter operations with ADS-B. I assume that area is class G / no surveillance now?

@DeltaLima Yeah only limited radar coverage over the North Sea. And class G up to FL85

The following is, in respect of aircraft, speculation. However, I did spend a decade working on the GPS based tracking systems mentioned in the question, with particular emphasis on remote operations in rural Australia. We did trial the use of Iridium, so I will comment on that too.
Firstly such systems do not report in real time, that is baloney put out by marketroids who don't even know what real-time means (I discovered this while trying to persuade them not to put unsupportable claims in promotional material.)
Vehicle positioning and telemetry systems report periodically. The more sophisticated units are store and forward, which means they log position at frequent intervals and upload bursts of telemetry as and when the network is available. The "real-time" ones use the telephone network, while others upload as they pass through WIFI waypoints, usually at depots and pickup locations. Hybrids exist, reporting sparse data periodically through the network and uploading higher resolution sampling at waypoints. The more sophisticated units have rules for priority.
Land freight in the United States runs along narrow concentrated corridors (roads and rails) that are well serviced by the telephone network. This is also true for freight on the eastern seaboard of Australia, but availability diminishes as you head west. As a result, the network is available most of the time so the units can upload at regular intervals, maintaining the illusion of real time tracking. Some systems also support manual polling of unit to obtain fresher position information on demand but this only works when the unit happens to be on the network.
When we tried it, Iridium had dismal bandwidth at outrageous cost. In the southern hemisphere, the satellite density is so low that you might see a satellite briefly every twenty minutes or so. The time between deciding things are out of control and the aircraft crashing could easily see the plane down before a satellite connection is available, although I suppose things might be better at high altitude with much wider horizons. The Iridium systems I had were power greedy, but that's not a problem in vehicle mounted systems.
Aircraft move too fast for the cellphone network; by the time they finish negotiating with one cell they're over the next. Also their altitude means they get similar signal strength from several neighbouring cells making them hop between cells unpredictably. I have been in a private plane in which the radio equipment failed, and the pilot had a devil of a time keeping a cellphone connection to the tower due to speed and altitude. Commercial craft are higher and faster so I doubt it would work at all.
Out at sea, there's just nothing but satellite comms. Over the Atlantic I imagine it wouldn't be too bad, but there are a lot of commercial routes that go a long way in the middle of big wet nowhere. Also there are a lot of commercial flights, and they move so fast you'd have to report every second to get any kind of positional precision. I'm not sure the civilian satellite network could cope. I know they stream vast amounts of TV data, but (a) that bandwidth is committed, and (b) that's loss tolerant streaming. It's high lag. When you try to use them to support non-loss network chatter the throughput plummets.
I have no idea why the black box isn't ejected prior to impact. You could easily set up a system that once armed would eject it when the craft dropped below a certain altitude. If it were me there'd be a little parachute and a self-inflating weather balloon, and the plane would be transmitting position updates to the ejected system until it failed. A little solar charger could keep the transponder going and with the balloon keeping the unit up off the water it shouldn't be hard to find. Such a system would have no network dependencies and although it might well drift a long way before being collected, it would know where it was at the time of ejection and exactly where the aircraft was when it ceased transmitting.
An interesting question from the comments:

Perhaps the aircraft could maintain an adaptive network between them
  as they fly around? That would increase the range of the coverage. The
  bandwidth for reasonably periodic position packets is low enough that
  one aircraft could easily forward packets from dozens of others, (and
  then on to base stations).

It's a nice idea but oceans are colossal. Even with hundreds of flights in the air at the same time, even in air corridors over land, being in visual range is a periodic event. Only in the crowded airspace around a commercial airport is this likely to work - and when you're that close you have comms anyway. A shame because it's creative and technically interesting.

How would the black box ejection system work?

Perhaps the aircraft could maintain an adaptive network between them as they fly around?  That would increase the range of the coverage.  The bandwidth for reasonably periodic position packets is low enough that one aircraft could easily forward packets from dozens of others, (and then on to base stations).

Great answer! About the TV satellites: The base stations on earth use  antennas each AWACS would be proud for. And the satellites themselves shape their beam to the region to be provided for a high signal strength. So, consumers have more dish-like that AWACS-like antennas. Outside the satellites footprint, receiving antennas again grow to AWACS dimensions. Geostationary antennas are far, far away, and you need big antennas.

Well, @sweber, aircraft actually do use geostationary satellites like Inmarsat for their data links. But the bandwidth is limited by smaller antennas and capacity of the satellites.

"I have no idea why the black box isn't ejected prior to impact.": Possibilities are: Keep the recorders and the airframe together to facilitate rescue and recovery; Ejection adds complexity, so failures; Unprotected in 10m waves, recorders have a hard time; They won't transmit without an antenna clear of metal and water, and a large battery that can deal with low temperatures and impact Gs; Maybe they could also be eaten by animals or damaged by ships. If something should be ejected, it must be an ELT.

Great answer from someone with experience in the field. Thanks for posting this! I'm not sure how I've missed seeing your answer, as often as this question bubbles to the top of the active list...

How can the pilot use radio communication with the air traffic controller if there is only satellite communication as you say?

@RonenFestinger - In some places they can't. Pilots know when they are in range because they know where they are, both from GPS and from flight time on a known speed and heading.

@mins - if you re-read my answer you will note that I suggested a way to keep the unit out of the water and to maintain power. The unit need only log the time of disconnection from aircraft electrics and the rest (position, heading and velocity) can be had from the tracking log. Many aircraft grade GPS units are capable of 10Hz sampling. To stop the log from rolling over (they usually use a big ring buffer) you would have to drop the logging interval significantly - perhaps wait for 10km displacement from last sample.

@PeterWone: Your answer is good in explaining the difficulty to get a radio link from water areas. But this part suggesting locating the aircraft with a detachable FDR acting as a transponder confuses me. The GPS position is already sent by the ELT using COSPAS/SARSAT, so the ELT should be ejected in your scenario. The FDR may remain with the airframe to be protected from ships, waves, low temperature, icing, etc (when ADS-B satellites will be deployed in a few years, a slow radio link will be available full time, and other solutions will be used).

Six years later: would the Starlink network allow (pseudo) real-time location transmission over oceans?

The main problem with this is that it is somewhat easy to know where the device is, it's a lot harder for the device to tell someone else where it is.  Satellites are really the only option for this sort of thing, and a lot of the polar routes have pretty poor satellite coverage anyways.  Also, satellite bandwidth is quite expensive.

Iridium has coverage even in polar region.

there is already something like that, the primary and secondary radars allows for positional data to be received by the controller, so adding this is superfluous from FAA's standpoint. To do this voluntarily is expensive.
To roll out a transmission of gps position data you need someone to be listening to it. Cars use the existing mobile network. Planes would likely use the transponder frequencies.
You also still need to be compatible to existing transponders while the global rollout happens.

What if they are out of radar range?

@JoelFan then you won't be able to receive gps data either unless you use satellites but that isn't cheep either

From a documentary on the 2009 Air France crash: I remember an aviation expert answering the same question. He said that it is expensive (About extra $300 million for a typical national carrier per year) and Airliners are reluctant to take on any additional expenses even if such an undertaking improves safety (The Air France jet crashed because the Pitot tubes froze thus disengaging the auto pilot. The Airline was aware that the Pitot tubes needed to be replaced way before the accident but did nothing because it was expensive).

that is not why AF447 crashed...

@Radu094: In a sense it is. A single fault will not take down an airliner, so there were many other failures (pilot failures to use proper procedure and to recognize the situation and appropriate correction measures), but the accident sequence was initiated by frozen pitot tubes.

Actually I don't think it's terribly difficult to implement technically. Of course getting regulators and airlines on board - and dealing with security and privacy issues are other matters entirely.
As others have pointed out there are existing satellite data networks (e.g. Iridium and Inmarsat) that can be used to transmit location information "back to base". The field terminal equipment for these networks isn't particularly power hungry either.
Infact a company I did a bit of work with in the past (on another project) sells a system exactly like that right now, which is designed for helicopters and small aircraft. They're not a big company, so I'd lay odds that they have competitors in this field too.
https://www.indigosat.com has details of their particular system.

For commercial aircraft, I don't see any privacy issues.

This service is already available for GA aircraft on VFR flight plans, using the consumer grade Spot Beacon.   (Link to Press Release).
Because Spot covers most of the earth, I cannot see why it wouldn't be a generalized solution.
The cost (at the GA level) is around \$100 for the device and about \$100 per year, so its quite reasonable.
The device is not covered by a TSO, so it is not certified for commercial use, and such a certification would be pricey and difficult.  Still, I think the technology is ready and has been demonstrated.

And according to their marketing material, they only send an update every 20 minutes, and they have no coverage at all over the polar areas. This doesn't sound super useful for aviation.

I have a Gen2 Spot, which sends updates every 10 minutes.  The newer Gen3 Spot can send updates every 2.5 minutes.    To me, that is plenty frequent, even for a commercial plane at 450 kts.   There just isn't that much traffic over polar areas to be of concern, and its certainly superior to the current lack of tracking.

No, it wouldn't be useful. And no, it would be exceedingly hard to implement, not to mention exceedingly expensive.
Cars and trucks are rarely out of range of cellphone towers, which is the system they use to transmit that data to their company headquarters. Mind that that's only used for some trucking and taxi companies, and a few car rental and lease companies, not generally (though there are some governments that are pushing for it, which has very strong privacy considerations as essentially your location would be known to the government within a short radius at any time, Big Brother is watching you...).
It's used mainly for fleet management purposes, like a rental agency can use it to pinpoint you to being where that speeding ticket was written so they can tell police who to send the fine to (and the points on your license).

The equipment for cars and trucks is also small, weighing in at maybe a pound (including mounting brackets, cables, etc.) and drawing little power.
For aircraft, it would need to be larger as instead of a small cellphone transceiver it would need a satellite radio link and antenna. It would also as a result draw a lot more power, which means higher fuel use on top of the extra fuel use from the higher weight of the aircraft (ignoring the possible extra drag from the antenna which makes it even worse).
And it's not real time, obviously, the cost would get to be far too high. Most cars and trucks would send an update only once every few minutes at most (selectable).

And aircraft already have something like it anyway, with systems that can send location and status data to the airline. But it's triggered manually, usually, and not in universal use.

Such a system would have virtually no purpose, and a high cost of operating it. You'd need not just a small box in every aircraft, you'd need a network of communications satellites, ground stations around the world with 24/7 staff on hand, etc. etc.
And I seriously doubt you're going to want to add a few hundred dollars to the price of every ticket just in the off chance that when your flight goes down someone can find the wreck a bit sooner.

you could use an existing satellite-phone network for the data,

I kinda have to disagree with "no, it wouldn't be useful" -- It's VERY useful when you can make it work...

So let me see if I understand your answer correctly:  You say that it isn't useful, it would be too expensive, has no purpose, and yet aircraft already have it??  I think I'm missing something....

A few hundred dollars on the price of every ticket? You're suggesting that no GPS tracking system could be built for a cost of less than tens of thousands of dollars per flight?

"your location would be known to the government within a short radius at any time" that's right, as if we were all carrying a cellular phone. hey wait..

"For aircraft, it would need to be larger as instead of a small cellphone transceiver it would need a satellite radio link and antenna. It would also as a result draw a lot more power, which means higher fuel use on top of the extra fuel use from the higher weight of the aircraft (ignoring the possible extra drag from the antenna which makes it even worse)."  I don't agree with this at all.  The commercially available SPOT Beacon can upload location every minute to satellites, weights approximately 1/2 lbs, and costs around $100.

You just need a simple satellite phone which will transmit automatically its gps location when the phone is experiencing high acceleration. cost is nothing compared to the price they pay for search teams which, and the guarantee that you find the reason of the crash.

I haven't read through all of these responses, but most focus on locating the plane going down in the middle of the ocean, as well as major new equipment and transmitters. First, the location wouldn't have to be a separate GPS transmitter. It only needs to be voice or text transmitting the location data which the plane already has. Whatever the communication of the location data, it doesn't have to be relayed at the point of impact or damage. Obviously, that would be most helpful, but in the case of MH370 - and especially if it was flying in a straight line, then having 2 points would be helpful.
That is, if the plane is detected over Malaysia, then over the Indian Ocean, they would have a path and relative search area based on fuel, etc. It's not perfect, but simply a transponder that can't be turned off would probably have been sufficient enough to detect the general area of the aircraft in the first week. There needs to be satellite tracking in real-time, but I think there are sufficient systems in place already that would have made this much easier.
As an example, and in response to the earlier post about \$300M system, if a person sat on a plane and texted lat/long every 15 seconds, they would find this plane much quicker even if it went beyond text towers. I'm not suggesting having a person do that, but you can create a device that does that for a relatively small amount of \$. It's not the perfect system, but is better than nothing.

This is a good answer, but it doesn't actually address the question of why this doesn't already exist.

As far as why pilots can turn off the transponder, see this question.  As far as texting your position, cell service doesn't work at altitude or over the ocean/other places where there are no cell towers.  It's the communication of the data, everywhere in the world, that is the main issue here.  If an airplane crashes in the middle of the US or Europe, you won't need anything on the airplane to find it....

As stated previously bandwidth cost and coverage of satellite communication accross the ocean is a major issue for something which doesn't directly make the airlines make money (contrary to in flight data for PAX). Even if you do it too often you could reach the limits of the actual satellite communication system.
This is well studied by the report made following the AF447 crash : http://www.bea.aero/en/enquetes/flight.af.447/triggered.transmission.of.flight.data.pdf
To reduce the cost of it the question asked is "can the plane transfer its position when it detects an unusual situation".

Some 400 aircraft already do this via the AFIRS system, which uses Iridium satellite constellations to communicate.  It costs some $100K to install.
Note that Inmarsat has a free tracking offer, free as in customers that are paying for services from third-party providers.  Doesn't have complete worldwide coverage.
As to why it hasn't been mandated, I do believe it has to do with necessity with cost benefit analysis / risk management vectors until recently not requiring it.  With the search costs of AF447 reaching 100M and the at least $80M spent on the MH370 search, the risk profile may now provide some impetus to install such technology.  If only to reduce cost exposure in the event of a loss and to gain the advantages provided by real-time monitoring of aircraft systems.
Bottom line is that it hasn't been seen as a necessity, but it is technological a reality already with some aircraft already carrying the systems.

Consider that radio line-of-sight horizon varies with altitude and transmission power.  I have not calculated the radio line-of-sight horizon from 30,000 to 35,000 feet but I imagine that it is staggering.
There are Ham radio operators listening for distress calls twenty-four hours a day, around the world. A distress call accompanied by GPS coordinates would get immediate attention from anyone on the frequency. Ham satellites are another resource.

while this might be an interesting consideration, I fail to see how this answer the question why they do not have it?


text:
Why is tailwind during final approach and landing so dangerous?
I understand that tailwind is typically a good thing during your flight as it increases your ground speed and gets you to your destination faster.  Despite that I get a feeling that pilots typically get very uncomfortable when there is a significant tailwind present during landing.  Sadly, recent proof of this danger was in Aspen, Colorado accident
Questions:

Why are tailwinds bad during landing?
Given "extra long" runway for extended rollout, are there any dangers with landing at a higher ground speed?
How are tailwinds mitigated?  Would ATC just switch the landing direction?

It's not so much a matter of "pilots typically get very uncomfortable" as it is "pilots recognize that it is an inherently less safe situation", and pilots (at least the ones you want to fly with) tend to be somewhat safety obsessed.

So Why are tailwinds during landing "bad"?
The same reason tailwinds in cruise flight are good: you're moving over the ground at a higher speed.
The amount of energy the aircraft has (and thus its landing distance) is roughly proportional to the square of the groundspeed.
Let's consider the plane I fly as an example (a Piper Cherokee) because I know the numbers:
if I'm flying by the book then when the wheels of my plane hit the ground my indicated airspeed should be around 45 knots.

No Wind
If there's no wind my ground speed and my indicated airspeed will be about the same - my brakes will have to slow me from 45 knots to a stop before I run out of runway.
The brakes on the Cherokee aren't Porsche brakes (they're tiny little things), but they're up to the task and a book-perfect landing would have me stopped in 600 feet.
15-Knot Headwind
A 15 knot headwind reduces my groundspeed to 30 knots - at 2/3 the speed I can stop much sooner with the same braking force, which means less wear on the brakes and a greater safety margin of runway remaining.
A book-perfect landing in these conditions would have me stopped in about 270 feet.
15-knot Tailwind
A 15 knot tailwind increases my groundspeed to 60 knots. The tiny little brakes on the Cherokee CAN stop me, but they're going to take much longer to do so: A book-perfect landing would take over 1000 feet to stop (nearly twice the "normal" no-wind landing roll).

The big consideration above is landing distance -- as you noted in your question you can solve that with a longer runway (more pavement means more room to stop), but there are other dangers with tailwind landings, mainly in the fact that Landings don't always go according to plan.
The slower your groundspeed at landing the less energy you have to get rid of if something goes wrong
Consider the three landings I outlined above, but let's add a problem to the mix: One of my tires blows right at touchdown, and the plane veers off the runway into a ditch.
There is much less energy to dissipate with a 15-knot headwind (30kt groundspeed) than there is with a 15-knot tailwind (60kt groundspeed) - it's roughly the difference between crashing your car driving through a school zone versus speeding on a highway.

Fortunately it's really easy to avoid landing with a tailwind -- most runways are bidirectional (Aspen, which you mentioned in your question, is a notable exception due to geography).
ATC (or at uncontrolled fields, the pilots themselves) will "turn the airport around" once a certain tailwind limit is reached.  Precisely when that happens depends on the airport and the traffic mix (at my home field, with mostly small piston aircraft, ATC will typically switch the runway when the tailwind component exceeds 5 knots - at JFK they might land a jet with a 10-knot tailwind rather than messing up the arrivals).
Of course there's nothing that says a pilot has to accept a landing with a tailwind: If the pilot is not comfortable with the conditions they can request a runway aligned so the winds are more favorable. (There is a somewhat famous case of an airline pilot at JFK who ultimately decided to declare an emergency to ensure a landing on a favorable runway).

Actually you can land either direction at Aspen, but you get pretty close to the terrain and they avoid it if possible.

Also, I was going to add an answer later but this one hits most of my points.  I would add one further thing though:  A tailwind will decrease control surface effectiveness more quickly than without one while you are still traveling faster.  This is particularly an issue with tailwheel aircraft, but it does affect all of them!

Also remember that the amount of energy that needs to be dissipated increases with the square of the speed.  To stop from 80kts takes 4 times the effort as to stop from 40kts.

@voretaq7, nice answer.  The physics makes sense.  And yeah I have heard of that JFK pilot, very ballsy!

One other thing that can be a consideration in larger aircraft is the brake energy limit.  Higher ground speeds may make you exceed it.  Oh, and you can also run up against your maximum tire speed as well!

Also, there have been crashes because a pilot is looking outside and notices he's going way too fast. Slows down, but with the tailwind, when he's going the "right" speed he stalls

The primary concern is the increased landing distance due to the increased ground speed. Landing & stopping distances increase more-than-linerally with each knot increase in ground speed. Given other dynamics of a landing aircraft this can be the straw that breaks the camel's back.
The perfect storm
True story. C-141 on approach with a tail wind - not so bad by itself. Add in a 7,000-ish foot runway and indicated airspeed a little high.

The aircraft didn't want to land so to speak because of the increased lift due to excessive indicated airspeed. Also any gust (differential) is added to approach speed. In other words, the plane could not get into a landing attitude due to excess lift.
Flying over the ground even faster due to 1, above, and the tailwind induced ground speed increase.
Pilot realizes he's floating too much and pushes down to get the plane on the ground.
Nose wheel touches down - but not the mains! Pilots don't realize this.
Pilot applies brakes and nothing happens, the mains still in the air and all. Panic begins.
The end of the runway is getting closer and the pilot aggressively applies the brakes.
The mains touch down and tires immediately begin to blow out, due the locked brakes.
The aircraft is departing center line due to tires blown out on one side.
Pilot struggles to maintain control as the aircraft nears the end of the runway.
Still too fast for safe taxiing, pilot attempts to turn the aircraft onto the last taxi way before the end of the runway.
Aircraft nose is turning but momentum, excess speed, drag from blown tires, differential braking - plane now slides sideways.
Aircraft stops just off of the end of the runway facing 90 degrees.
Aircraft catches on fire. That it's on the side of the blown tires and dragging strut is no surprise.
Everyone gets out safely.
NOTAM issued warning aircraft to beware the burned out hulk at the end of the runway. Adjust TakeOff and Landing Data accordingly.

And the worst part of all of this?

It was to be the aircraft commander's "fini flight" - his last (multi stop) mission before leaving the Air Force. And so it was, only more so.

What did the aircraft catch on fire from?  Did one of the wingtips hit the ground while it was sliding?

The heat from locked brakes, shredding heated tires, gear strut disintegrating. The aircraft did not break apart. I believe confined pretty much around that wheel well and wing root. The plane was not burned to the ground and the wings were in in tact. I got only a couple of seconds to glance down as we flew over it.

As others have highlighted, the question is with what ground speed you touch down. You might think that plus/minus a few knots doesn't really matter, but:

your kinetic energy is quadratic in speed: E = 1/2 m v^2.
if braking acceleration is constant, landing distance is quadratic in speed: s = v^2 / 2a

So, to adapt voretaq7's example, if your approach air speed is 45 knots, with a 15 knots headwind you land with 30 knots, while with a tailwind you land with 60 knots - now you touch down with four times the energy you need to dissipate, and need four times as much runway to stop (which, happily, lines up nicely with his POH numbers).
Now, finally, one more example:
Suppose the runway is such that with no wind, you can land with approach speed v and just stop prior to the end.
With a (mild) headwind of 10% of your airspeed, you touch down with 0.9v, thus you now use only 81% of the available runway, and have gained quite a buffer.
Whereas, if you have a 10% tailwind, you touch down with 1.1v. Thus, your required stopping distance now is 1.21 times the available runway. When you hit the end now, you'd need 21% of the runway length extra to stop. Now, this gets a bit tricky, but feel free to do the maths, this means that you hit the wall at the end with nearly half of your approach speed, still having about 21% of your (1v) landing energy left to dissipate.
So - what would you rather have, a 20% buffer of runway remaining (with head wind), or hitting the end of the runway with over 40% of your landing speed (with tail wind)? :-)

To answer in part the question of how tailwinds are sometimes mitigated, an air carrier's op specs will typically specify how much of a tailwind is allowed for their operations. The two 747 carriers I flew for allowed a max tailwind of 10 knots.
Whether a captain should choose to land given the max tailwind can be a complicated call. For example, runway 02 at Nadi, Fiji is about 9,000 feet, which makes it a bit of a short field operation for a 747 landing at or near max landing weight, a common occurrence with freighters. In the instance I'm thinking of, we were well inside the outer marker when the tower told us the wind had switched and that there was now a 10 knot tailwind.
I chose to land and here's why:

To have gone around would have meant involving ourselves further with the thunderstorms around the field.
There was no guarantee that when we approached from the opposite end the wind would not have switched again and we would again be landing with a tailwind.
Having landed there many times, I knew our spot on the ramp was very close to the end of the runway, there would be less than a minute of taxi time.
I knew the Nadi ground service people were used to using a huffer on hot freighter brakes.
I told the flight engineer to call the ground service people and tell them that we would have very hot brakes.

747 tires have 225 psi tires filled with nitrogen, and each tire has a thermal plug that will blow before a tire does. The QRH for handling hot brakes included instructions to warn the ground crew not to stand to the side of the tires, but the Nadi people were well aware of that.
All brake temperature gauges went into the red. I got out of the airplane as quickly as possible to take a look. They already had a huffer on each side of the airplane blowing on the brakes.

because the ground speed would be greater than your airspeed, something you do not want during landing (or take-off): you need at least a certain airspeed to have enough lift, and tailwind would make you too fast w.r.t. ground, making your landing distance much bigger than actually needed
it depends on how much "extra long" and how much "higher ground speed", the aircraft manufacturer will have included tables in the Pilot Operational Handbook, you will have to consult them to verify if it safe or not.
yes, it is indeed switched.

Just an additional human factors flavored aspect:
Your speed relative to the runway is greater than usual. If you start adjusting your relative speed by your usual (headwind) visual reference, this might well lead to a stall situation - never a good thing close to the ground.

With a really good headwind and a little bitty plane (Cessna 150) you can get your groundspeed down to a trot and and just set it on the ground.  Have done it at PDK in Atlanta, in March.
Do not do this with passengers. Safety is one reason.  Not terrifying them is another.

I've heard numerous anecdotes of C150s landing across the runway when the crosswind component was too high to land conventionally.

An additional issue is that as you descend through the wind gradient-- into the slower-moving air near the ground-- with a tailwind, the aircraft will react just as if it is experiencing an increasing headwind-- it will really want to float.  The sink rate will be decreased.
Then when the pilot recognizes his mistake and adds power to go around, the aircraft has to climb up through the wind gradient again.  Now the effect is the same as a decreasing headwind-- the climb rate is lousy.
Harnessing these sorts of effects is what "dynamic soaring" is all about-- as practiced chiefly by albatrosses (the birds not the WW1 biplanes.)
One side effect of the extra "floatiness" while landing with a tailwind, due to the wind gradient, is that the actual touch-down tends to be really "greased on" even with less-than-perfect technique on the pilot's part.  If you don't want to risk life and limb exploring this effect in a full-sized airplane, you can do it with a radio-controlled model-- make an abbreviated landing pattern with a "hairpin" turn back to the runway after each takeoff, so you can alternate between upwind and downwind landings.  You may be surprised at how the downwind landings tend to be consistently smoother than the upwind ones.
One bad scenario is if you are taking off (perhaps after a "touch-and-go" landing) with a nearly direct crosswind, and you accidentally let your heading turn to point toward the downwind edge of the runway.  Now your groundspeed is higher than normal, AND the wind gradient is working against you as you try to climb out.  The odds of hitting something are much, much higher than if your had veered in the opposite direction, into the wind.  And if you DO hit something, you'll hit it with a lot more kinetic energy than if you had veered in the upwind direction.
Pilots of lightweight, slow-flying aircraft need to allow plenty of extra airspeed for the round-out and flare, when landing into the wind in the presence of a strong wind gradient.  During the last ten feet or so of descent, the airspeed has a tendency to vanish-- not a good thing if the flight path is still aimed steeply downward.

" During the last ten feet or so of descent, the airspeed has a tendency to vanish--..."-- this of course is the opposite of the "floatiness" experienced when landing downwind